1. Technical Field
The present technology pertains generally to biological and chemical sensing devices and methods of use, and more particularly to an optical sensor based on a high contrast grating coupled with a surface plasmon polariton platform. The high contrast grating facilitates high optical coupling efficiency with a large tolerance of the interrogating optical beam with the surface plasmon polariton waves and improves the quality factor of the optical resonance, which in turn improves the sensitivity of the overall device.
2. Background Discussion
Laboratory assays such as, polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA) and cell culturing methods are highly sensitive techniques that are available for the diagnosis of infectious diseases. However, these techniques require transportation of the sample to the lab, manual preparation steps, and skilled laboratory technicians to perform and read the assays. As a consequence, these techniques provide results in several hours to several days and are not capable of rapid detection. These techniques are also not capable of detecting or identifying multiple infectious agents such as bacteria and viruses at the same time.
Biosensors can provide label free detection of biomolecular or chemical interactions and have applications in medical diagnostics, environmental safety, bioterrorism, biomedical research and drug discovery. Generally, biosensors have an interaction sensing element that interacts with a target, a transducer that the transforms the sensed interaction into a readable optical, acoustic electrical, piezoelectric or similar signal and a read-out system to interpret the produced signal. The signal readout can be transformed into meaningful diagnostic information for a practitioner very quickly compared with existing assays.
Biosensors may be classified either by the type of biological sensing mechanism that is utilized or by the type of signal transduction that is employed. Typical biological signal mechanisms include a recognition element that is an immobilized biocomponent that is able to detect a specific target analyte.
Biological recognition mechanisms may include antibody/antigen, enzyme/substrate, nucleic acid sections and chemical adsorption or binding. The recognition mechanisms may also include interactions between the target and receptor that bring about chemical changes such as the production of a new molecule, the release of heat, the flow of electrons or changes in pH or mass.
The transducer is a device that needed to convert a wide range of physical, chemical or biological signals into an electrical signal with high sensitivity and reliability and plays an important role in the signal detection process of the biosensor. There are five main types of biosensors determined by the nature of the biological signal that is transduced.
Optical biosensors detect light produced, reflected, transmitted or absorbed during the interaction with the sensing element. Optical sensing platforms employ various methods, including refractive index change monitoring, absorption, and spectroscopic-based measurements. Potentiometric biosensors detect the production of an electrical potential due to a change in the distribution of electrons through bonding or adsorption etc. Acoustic wave biosensors are based on the detection of a change in mass from the reaction of a biological component of the sensor and the target. Amperometric biosensors can detect the movement of electrons due to the presence of redox reactions. Calorimetric biosensors detect heat that is absorbed or released from the reaction of the sensor and the target.
Transducer signals may then be processed through microelectronics and a data processor, amplified, interpreted and then displayed. Processed signals and results can also be recorded and historical data that is acquired over time can be compiled and displayed.
However, there are limitations to both the recognition elements and transducer devices that are used in the wide variety of biosensors that have been developed. For example, the biological material that is selected for use on the recognition element may denature under environmental conditions (e.g. pH, temperature or ions) or produce a faint or contaminated biological signal.
Some commercial microarrays rely on the detection of labeled target molecules. However, the labeling process complicates the sample preparation, detection process, and also may change the molecule's binding properties, which may compromise the detection accuracy and reliability of the biosensor.
Transducer platforms may also have inherent detection, conversion or sensitivity limitations in the conversion of the biological signals into electrical signals. For example, fluorescence detectors may have difficulty detecting low intensity emissions or low numbers of bound targets may not produce a physical change that is detectable by the transducer.
Accordingly, there is a need to develop more efficient, sensitive and reliable transduction and detection technologies. There is also a need for new diagnostic devices and assays that have quick response times, that are label free, are highly sensitive and selective and are inexpensive to produce and operate.